Reverse shuttling in a fullerene-stoppered rotaxane

The preparation and characterization of a solvent-switchable rotaxane that shuttles in the opposite direction to that expected are reported. The reverse shuttling is confirmed by NMR spectroscopy and can be monitored by cyclic voltammetry. The electrochemically generated anions on the fullerene moiety are stabilized by the closer proximity of the macrocycle.     

Thermodynamic properties of gold–water nanofluids using molecular dynamics

Conflicts and discrepancies around nanoparticle (NP) size effect on the optical properties of metal NPs of sizes below the mean free path of electron can be traced to the internal damping effect of the hybrid resonance of the inner band (IB) and the conduction band (CB) electrons of the noble metals. We present a scheme to show how alternative mathematical formulation of the physics of interaction between the CB and the IB electrons of NP sizes <50?nm justifies this and resolves the conflicts. While a number of controversies exist between classical and quantum theories over the phenomenological factors to attribute to the NP size effect on the absorption bandwidth, this article shows that the bandwidth behavior can be well predicted from a different treatment of the IB damping effect, without invoking any of the controversial phenomenological factors. It finds that the IB damping effect is mainly frequency dependent and only partly size dependent and shows how its influence on the surface plasmon resonance can be modeled to show the influence of NP size on the absorption properties. Through the model, it is revealed that strong coupling of IB and CB electrons drastically alters the absorption spectra, splitting it into distinctive dipole and quadrupole modes and even introduce a behavioral switch. It finds a strong overlap between the IB and the CB absorptions for Au and Cu but not Ag, which is sensitive to the NP environment. The CB modes shift with the changing refractive index of the medium in a way that can allow their independent excitation, free of influence of the IB electrons. Through a hybrid of parameters, the model further finds that metal NP sizes can be established not only by their spectral absorption peak locations but also from a proper correlation of the peak location and the bandwidth (FWHM).     

NO adsorption on the Rh(110) surface: kinetics and composition of the adlayer studied by fast XPS

The adsorption and dissociation of NO on the Rh(110) surface were studied by synchrotron radiation X-ray photoemission spectroscopy at temperatures in the range 210–370 K. The O 1s or N 1s spectra were collected every 14 s while the surface was continuously exposed to a steady NO gas pressure. The difference in the binding energies for the atomic oxygen (O 1s ≤530.2 eV), atomic nitrogen (N 1s 397.2 eV) and molecular upright bonded NO molecules (O 1s ≥531.0 eV and N 1s 400 eV) allowed us to distinguish these surface species and to follow the evolution of the adsorbate layer. In addition to these dominating surface species a new species, characterized by O 1s binding energy of 530.7 eV and N 1s binding energy similar to that of the atomic nitrogen, was detected within a narrow coverage range. This state is tentatively assigned to a “lying down” NO bonding configuration, detectable at the timescale of the measurements. The uptake plots, constructed using the integrated intensity of the deconvoluted O 1s and N 1s spectra, are used to elucidate the effect of the reaction temperature and surface coverage and composition on the kinetics of dissociative and molecular NO adsorption of Rh(110).     

Deracemization and Transacetalization of Aldehydes with Enantiomers of Betti's Base Derivatives

Improved procedure for the deracemization of α-methyl dihydrocinnamic aldehydes (2-methyl-3-phenylpropanals) with L-(+)-tartaric acid salt of (S)-enantiomer of Betti's base, is presented. The method enabled the transacetalization of N,O-ketal (R)-enantiomer of Betti's base with various aldehydes.     

Uniform Functionalization of High-Quality Graphene with Platinum Nanoparticles for Electrocatalytic Water Reduction

Graphene–metal composites have potential as novel catalysts due to their unique electrical properties. Here, we report the synthesis of a composite material comprised of monodispersed platinum nanoparticles on high-quality graphene obtained by using two different exfoliation techniques. The material, prepared via an easy, low-cost and reproducible procedure, was evaluated as an electrocatalyst for the hydrogen evolution reaction. The turnover frequency at zero overpotential (TOF₀ in 0.1 m phosphate buffer, pH 6.8) was determined to be approximately 4600 h⁻¹. This remarkably high value is likely due to the optimal dispersion of the platinum nanoparticles on the graphene substrate, which enables the material to be loaded with only very small amounts of the noble metal (i.e., Pt) despite the very highly active surface. This study provides a new outlook on the design of novel materials for the development of robust and scalable water-splitting devices.     

Adsorption of oxygen on Rh(110): a LEED, Auger electron spectroscopy and thermal desorption study

The adsorption of oxygen on the Rh(110) surface has been studied by a variety of techniques. Low-energy electron diffraction shows the following patterns: (2 × 1)p2mg at 1 ML coverage and temperatures between 125 and 300 K; (2 × 2)p2mg at 0.5 ML coverage after heating to above 470 K; c(2 × 8) and complex streaked c(2 × 2n) patterns at coverages above 0.5 after heating to 470 K. These results are in partial agreement with previous work. Models for the first two structures are suggested. In the (2 × 2) structure, the oxygen is found to be much less reactive with CO at room temperature than in the (2 × 1) structure, suggesting that it is subsurface. A metastable (1 × 2) structure was produced from the (2 × 2) by reduction of the oxygen by CO at 450 K, and is interpreted as a surface reconstruction.     

Unexpected behavior of the surface composition of PtRh alloys during chemical reaction

The changes in the surface composition of a Pt(50)Rh(50)(100) alloy due to an ongoing 2H(2) + O(2)-->2H(2)O chemical reaction have been studied in situ. Exploiting the high-energy resolution and surface sensitivity of synchrotron radiation core-level spectroscopy it was possible to monitor the population of the two transitions metals atoms at the gas-surface interface. Sequences of fast high-resolution core-level spectra of the Rh3d(5/2), Pt4f(7/2), and O1s core levels showed a continuous exchange of atoms between the first and subsurface layers. An unexpected Pt surface enrichement was found under slightly oxidizing conditions, opposite to what found in a highly oxidizing atmosphere.     

Synthesis and hydrolysis of substituted imidazolinium salts. Behaviour of the degradation products on varying pH

Reaction of l-alkyl-2,3-diarylimidazolinium iodides 1a-i with alkaline solutions afforded N'-alkyl-N-aroyl-N-arylethylenediamines 2a-i. Compounds 2 are stable under acid conditions but in neutral or alkaline media rearrange giving N-alkyl-N-aroyl-N-arylethylenediamines 3a-i. Treating compounds 3 with concentrated acids reverse reaction 3 → 2 takes place. Kinetic studies were performed on this intramolecular N → N' aroyl transfer over the H_o-pH range ?0.9 to 2.30. Compounds 3 undergo acyl transfer to give 2 by a mechanism which involves a change in the rate determining step from formation to catalysed decomposition of a heterocyclic intermediate I ²⁺ on going from H_o to pH values. The existence of maxima in the pH rate profile allowed to determine apparent pK_a values of the imidazolidine intermediates which gave good correlation with Hammett sigma values. Stability of these heterocycles was also predicted by determination of thermodynamic parameters.